This invention relates to electro-optic imaging members and, more specifically, to multi-layered imaging members including a deformable elastomer layer and a thin flexible, conductive metallic layer. The invention also relates to methods for forming the metallic layer and imaging methods utilizing the novel imaging members.
There is known in the imaging art a broad class of imaging members which record optical images by an imagewise distribution of photogenerated voltages or currents acting upon a voltage or current-alterable recording medium. Typically, in these members, imagewise activating radiation incident on a photoconductor allows charge carriers to move in an external electric field. These charge carriers interact with a voltage or current-sensitive member which, in turn, modulates light.
U.S. Pat. No. 2,896,507 describes an imaging member which includes a photoconductive layer and an elastically deformable layer sandwiched between a pair of electrodes, one of which is a thin metallic layer overlying the deformable layer. In operation, imagewise activating radiation is directed upon the member and an electrical field is established across the photoconductive and deformable layers thus causing these layers to deform in imagewise configuration. The member is described as being capable of functioning as an image intensifier since the deformation image may then be read out with a high intensity light source and a schlieren optical system.
Devices of this type are of great interest because of the many applications in which they may be utilized such as, for example, image intensification, image storage, etc. Of course, for commercial purposes these devices typically should be capable of a great many imaging cycles, for example, at least about 100,000 and preferably many more. For satisfactory performance, many demands are imposed upon the metallic electrode layer. This thin metallic layer desirably should be highly reflective to utilize the read out light efficiently; have good lateral conductivity since, as one electrode of the device, it should allow charge exchange with all points of the device; be highly flexible in order that the imaging deformations can occur without any impediment at the operating conditions; have excellent stability, i.e., its imaging properties should not change substantially during shelf storage or under repeated cycling; and have little internal stress since, for example, any appreciable tension would typically tend to reduce the maximum deformation and also tend to shift it to lower spatial frequencies. An important requirement is that the metallic layer should be adherent to the deformable layer so as to couple efficiently the deformations of the metallic layer to those of the deformable layer.
It should be noted that U.S. Pat. No. 2,896,507 is completely silent as to materials which may be used for the metallic layer and also as to methods for forming the metallic layer on the deformable layer. It will also be appreciated that enormous problems are encountered in providing metallic layers which are capable of satisfying the demands imposed on them. For example, in such thin layers some metals may be highly reflective but may not be sufficiently conductive.
Recently, a major advance in the art was made by Sheridon who disclosed the Ruticon (derived from the Greek words "rutis" for wrinkle and "icon" for image) family of imaging members wherein the voltage-sensitive, light modulating recording medium comprises a deformable elastomer layer and the photoconductive material may be provided as a separate layer or incorporated in the elastomer layer. (For a detailed description of the Ruticon devices see IEEE Transactions On Electron Devices, September, 1972, and U.S. Pat. No. 3,716,359). Various different embodiments for establishing an electric field across the elastomer layer are described.
In the embodiment referred to by Sheridon as the Gamma Ruticon, a thin flexible metallic layer is provided on the surface of the elastomer layer and serves as one electrode for the device. Sheridon's Gamma Ruticon is capable of excellent performance for a great many imaging cycles, because, inter alia, the flexible metallic layer is capable of satisfying the stringent requirements placed on it. Sheridon obtains this desirable result by forming metallic layers comprising a plurality of different metals. The preferred metallic layer composition comprises gold and indium. Other metals suitable for use in the metallic layers of the Gamma Ruticon devices are also disclosed (see particularly Column 10, lines 1-8 of U.S. Pat. No. 3,716,359). It is also disclosed that other materials may be added to these layers to enhance or suppress particular characteristics. Various techniques for forming the metallic layer on the elastomer layer are described including, for example, by vacuum evaporation.
Although, as aforesaid, the metallic layer compositions disclosed by Sheridon are capable of excellent performance, it is always desirable to improve certain operating characteristics of such metallic layers. In relatively new and growing areas of technology, such as electro-optic imaging members including a deformable elastomer layer, new materials for use in these members continue to be discovered. The present application relates to a new and advantageous flexible metallic layer composition.